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Why do my pneumatic valves keep failing?

Pneumaticvalveblog 420x280 C, HS Innovations

If you posed that question to me, I would equate it to the age old question “How high is up?” In other words, the question is too open-ended. There are so many varieties of hydraulic valves and so many ways of failures that there could be a book to show all of these valves and modes of failure. I will describe some generic forms of valves and failure here, hopefully enabling you to look at your system in a more informed way.

Hydraulic, Pneumatic, or Process Fluid? What is flowing through the valve? The process fluid valve could have nearly anything liquid or gas at nearly any temperature passing through it.

Directional, Flow Control, or Pressure Control? The major classes of fluid power valves (could be applied to process valves also) from which all other types come fall under.

Electrical or Non-electrical Actuation? Seems simple, doesn’t it? If there are any wires, it’s electrical. If no wires, it’s non-electrical. Non-electrical does not necessarily mean manually operated, however.

You may think that the above descriptions are so simple that it’s ridiculous to even list them in such a manner. You’d be amazed at how many people cannot answer even those three simple questions. We will limit this blog to just the fluid power valves, and after a brief discussion about pneumatic valves, we’ll focus on just the hydraulic valves.

3 way air shut off valve with pressure bleed off

HSI’s Regulated Air Prevent Valve

Pneumatic valves control compressed air or vacuum. The condition of the compressed air many times determines the life of the valves in the plant. In a proper installation, the air supplied to the valve will go through an FRL before getting to the valve. An FRL (Filter-Regulator-Lubricator) should have a safety exhaust valve installed upstream so this branch can be safely isolated for maintenance.

A Filter-Regulator may be in one body, so you only see two individual components. Clean, lubricated air will allow a pneumatic valve to operate for a very long time. You must be aware that any oil mist put into the compressed air stream will also be exhausted out of a directional valve, so in food processing applications, this oil mist must be captured and filtered and not allowed to exhaust oil mist into the surrounding area.

Some very small pneumatic solenoid directional valves can be directly operated, but most are pilot operated. Typically, a pilot operated valve needs a minimum of 2 bar (29 psi) supply pressure to operate with an internal pilot supply. For regulated air below this pressure or vacuum applications, you must have an external pilot air supply that the small solenoid pilot valve actuates, using air to actually move the main spool of the directional valve. The same valve can typically be used for either variation, provided that a plug or gasket is in the proper position.

And of course there are some pilot operated valves that use diaphragms instead of a spool to control the air flow direction, and this type of valve does not require lubricated air. Still others use poppets instead of spools or diaphragms. Also, many of the solenoid operated valves have a manual override on the pilot air signal, an easy method to see if you have a failed solenoid section (or lack of an electrical command signal).

The modes of failure on a pneumatic valve are typically limited to dry, contaminated air, lack of an electrical command signal, or even lack of an air supply. A new valve installation that doesn’t work may be simply that the valve is not set up properly for that installation (internal vs. external pilot, i.e.) In a washdown area, it is typical that the actual coil on the solenoid valve may have failed.

Check back later this week for part 2 to this blog: “Why do my hydraulic valves keep failing?”

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